select DATE_FORMAT(Y_CDATETIME,‘%Y%m%d %H‘) HOUR,count(*) as ‘总量‘
FROM orderdata
WHERE  Y_CDATETIME >=‘2017-04-27‘
and Y_CDATETIME < ‘2017-04-28‘
GROUP BY HOUR;

SELECT *
FROM(
select DATE_FORMAT(Y_CDATETIME,‘%Y%m%d %H‘) HOUR,count(*) as ‘AA‘
FROM orderdata
GROUP BY HOUR
) t 
ORDER BY t.AA DESC;